Will the gas ratio of the standard gas or mixed gas change when the standard gas or mixed gas is stored for a long time without being used? In fact, if it is stored for a long time without using, there may be layering between the gases, resulting in a decrease in the accuracy of the gas, so when using it, we generally need to let him mix first.

Uniformity is an important indicator for investigating the performance of standard gases. The characteristics of the standard gas should be uniform, that is, its value is guaranteed to remain unchanged within the specified range. Regardless of which method is used to prepare the standard gas, it needs to be mixed. The standard gas mixing methods include: heat treatment, steel cylinder rolling method, special filling method, natural diffusion method, other mixing methods, etc. Several mixing operation methods are as follows:

Heat treatment method:

Generally, the prepared standard gas container is heated in a warm water bath below 40°C, so that the gas components are quickly mixed and uniform.

Cylinder rotating and rolling method:

Place the cylinder horizontally on the half-placed rolling shaft of the mixing, so that it rotates around the shaft center. This method requires short mixing time and simple operation.

Special filling method:

When filling some gas, the cylinder can be inverted and kept at a 45°C inclination, and inflated from the lower end to promote the adiabatic expansion of the gas and produce an exothermic effect. The gas can be mixed evenly while filling.

Natural diffusion method:

The steel cylinder filled with the standard gas is placed upside down at a suitable position, and it is still. The natural diffusion of the gas is used to achieve uniform mixing, but this method takes a long time.

Other mixing methods:

Using a static mixing vessel or using a specially constructed vessel valve can make the standard gas uniformly mixed in a short time.

No matter which method is used for mixing, another high-precision analysis method must be used for inspection. In the standard gas research stage, the uniformity of the studied standard gas should be investigated. Generally, gas chromatography is used to determine the uniformity of the standard gas under the same operating conditions, and the uniformity inspection method of the average value is usually used. judge. Since the uniformity is to investigate how long the measurement value of the same bottle of standard gas is stable after the preparation is completed, the average value obtained from a limited number of measurements should be insignificant within the uncertainty range of the method. If the difference is significant, this factor is caused by the inhomogeneity of the standard gas.